Yes, they bought any supply they could get their hands on. Also, it's not true that Nvidia cards were generally better for (Eth) mining. The Radeon VII for example outclassed Nvidia cards sold at the same time. It's just that Nvidia was able to supply more cards, since they had won the bigger gaming marketshare a while ago and thus were producing more.
Yeah, I'm going to be honest: I'm a cryptocurrency doomer so I've not followed things super closely, but a quick Google search turned up this article[0] from 2022:
>While it is true that Nvidia cards are generally preferred by miners due to better price-to-performance, AMD GPUs such as the Radeon RX 6600 XT could still be mined on profitably until recently. […] So yes, carefully consider the condition of all used graphics cards—Nvidia or AMD.